1. Field of the Invention
The invention relates generally to methods and systems for determining wind chill temperature. More specifically, the invention includes methods and systems for determining the wind chill temperature and the time to freeze for the facial temperature.
2. Description of Related Art
The sensation upon exposed skin that the ambient temperature in the presence of wind feels colder than the actual measured temperature is often referred to as the wind chill temperature. The concept of “wind chill” was first proposed by Siple, P. A., and C. F. Passel, “Measurements of dry atmospheric cooling in subfreezing temperatures”, Proc. Amer. Phil. Soc., Vol. 89, No. 1, pp. 177-199, 1945. The Siple and Passel experiments and model have been criticized by investigators as being primitive, flawed and lacking a theoretical basis. However, the Siple and Passel experiments yielded results that have proven useful for six decades. One criticism of the Siple and Passel model is that it incorrectly assumes a constant skin temperature of 33° C. (91.4° F.) during the entire time of skin exposure. This assumption was known to result in predicted values of the wind chill temperatures that would be colder than the actual values.
Despite this criticism, Osczevski, R. J., “The basis of wind chill”, Arctic., Vol. 48, No. 4, pp. 372-382, 1995, gave credence to these predictions when he stated that the test cylinder used by Siple and Passel was nearly the perfect size to represent the human head. This may explain, at least partially, why these predictions have served so well over the intervening years.
Wind chill temperature is an actual temperature that it is not restricted to the winter season. The wind chill temperature sensed by an individual on a windy, cold winter day is, conceptually, no different than that which he senses in front of an electric fan on a hot summer day. From a health or safety standpoint, the wind chill temperature sensed in the winter is the one which causes concern. The reason for this is the subjective nature of this temperature, i.e., the temperature sensed by one person may be quite different from that sensed by another. This is believed to be especially true at very low temperatures where a noticeable difference between the actual and perceived temperatures may be quite difficult.
Individual differences in sensing these low temperatures have led to proposed solutions on how the subjective nature of this temperature could be minimized. Suggestions have been made that the wind chill temperature should be replaced with categories such as “cold”, “very cold” and “extremely cold” or combining it with the heat index to come up with comfort index categories ranging from “minus to plus 10”. However, these approaches are also very subjective. Fortunately, neither of these proposed solutions has prevailed.
The subjective nature of the wind chill temperature has led to suggestions that it should be combined with clothing distributions to define a comfort level to which an individual can more easily relate. Because the comfort level is determined by the warmer temperatures sensed by the clothed surface of the body, this approach could mask a potentially dangerous situation. This could occur if the individual feels so comfortable, as a result of being adequately dressed, that he is unaware that his face may be subjected to the most imminent hazard of extended exposure, i.e., frostbite.
A more recent development is the wind chill model disclosed in Bluestein, M. and Zecher, J., “A new approach to an accurate wind chill factor”, Bull. Amer. Meteor. Soc., Vol. 80, No. 9, pp. 1893-1899, 1999. The National Oceanic & Atmospheric Administration's National Weather Service adopted the Bluestein and Zecher wind chill model on Nov. 1, 2001. Developed as an analytical counterpart to the Siple and Passel experiment, the Bluestein and Zecher model corrected for the constant skin temperature assumption by allowing it to vary, i.e., decrease with increasing exposure time. This was expected to give correct wind chill temperatures that were warmer than the Siple and Passel values. In addition, Bluestein and Zecher used a wind speed reduction at head level based upon the assumption that the free-stream velocity is always 50% greater. With this assumption and the skin temperature correction, the Bluestein and Zecher model does indeed predict wind chill temperatures that are as much as 15° F. (8.33° C.) warmer than the corresponding Siple and Passel values. However, a close examination of the Bluestein and Zecher results shows that essentially all of this warming is due to the wind reduction at head level with, at most, 2° F. (1.1° C.) being due to the varying skin temperature. At very low temperatures and high velocities the Bluestein and Zecher results show no moderation whatsoever. Instead of a moderation, their wind chill temperatures are approximately 1° F. (0.56° C.) colder than the Siple and Passel values. This result calls into question the accuracy of the Bluestein and Zecher model. Unfortunately, the Bluestein and Zecher model assumes that the free-stream velocity is always 50% greater than that at head level. Boundary layer calculations for all individuals in real life situations show that this 33% reduction in the velocity at head level is a unique condition which will almost never exist; in fact analyses will show that in all instances the reduction will be at or near zero. Without this incorrect velocity reduction, Bluestein and Zecher's results are actually no different than those of Siple and Passel.
Various devices have been proposed for determining wind chill temperature using the conventional methods disclosed by Siple and Passel, Bluestein and Zecher and others. Such conventional wind chill temperature devices are disclosed in U.S. Pat. No. 3,753,371 to Anderson, U.S. Pat. No. 3,954,007 to Harrigan, U.S. Pat. No. 4,047,431 to Mulvaney et al., U.S. Pat. No. 4,106,339 to Baer, U.S. Pat. No. 4,261,201 to Howard and PCT Patent Application No. WO 81/00462 to Howard. Generally, these devices are based on measurements of air temperature and wind speed only. Moreover, none of these conventional devices appears to correct for the above-noted errors in the prior art methods. Furthermore, the inventors are not aware of any methods or systems that account for other important factors such as altitude, insolation, and metabolic heat generation.
For the above reasons, it would be highly advantageous to provide a more accurate and complete wind chill model. It would also be advantageous to provide a system and method for wind chill determination based on a more accurate and complete wind chill model.